GIS-SUPPORTED ANALYSIS OF THE RIVER CHANNEL EVOLUTION OF SOUTH BRANCH IN THE YANGTZE ESTUARY FOR THE RECENT 100 YEARS

Quantitative analysis was performed on the evolution characteristics of the river channel of south branch in the Yangtze estuary for the recent 100 years with the help of GIS and DEM technology. Supported by GIS, five pieces of charts of south branch from 1900 to 2001 are digitized and digital elevation model (DEM) of south branch in different periods is established with Kringing gridding method, based on which the evolution of the river channel of south branch is visualized and the characteristics of erosion-accretion are calculated. The results show that (1) The river channel storage volume increased slightly at the annual average rate of 0.027×10⁸ m³, which coincided with the state of slight erosion of south branch at the annual average rate of 0.033×10⁸ m³ of volume and 0.37 cm of thickness respectively from 1900 to 2001, and the states of erosion-accretion were different in different terms and different locations, scouring before 1958 and after 1979 whereas filling from 1958 to 1979. (2) The evolution of south branch was characterized by the changes of five channels and four shoals with the area and volume of shoals and the maximum of depth of channels increasing respectively. (3) Most of cross sections in south branch were double-entry channel and the master channels located at south bank. Changes of cross sections at the entrance and exit were more intense than that of counterpoints in the middle of south branch. (4) The effect of floodwater-building channels and different waterway between flood tide and ebb tide were the two major natural factors on south branch evolution, whereas its response to suspended sediment discharge from Yangtze drainage basin reflected the influence of human activities on its evolution.